(1) Field of the Invention
The invention relates to an underwater imaging system for use in controlled environments such as acoustic test facilities. More specifically it employs a single fixed hydrophone receiver location and a rotated target to greatly reduce the amount of acquisition hardware required and can satisfy the fractional wavelength phase coherence requirements for imaging. Since the same test setup, and in many cases even the identical data set, can be used for other test purposes such as target strength measurements, the images can be used to help locate major contributors to target strength, and to indicate the position of the object relative to the data set used for the target strength measurements.
(2) Description of the Prior Art
Acoustic test facilities generally do not have any acoustic imaging capability. The Navy has long used such facilities for target strength measurements, target classification experiments, and acoustic calibrations. It would be advantageous to be able to image the target acoustically with the identical data. In these facilities, tests typically generate recordings of echo data, so that an imaging system based on reflection rather than transmission of sound is desirable. Test sites typically have facilities for accurate placement and recording of only a very small number of hydrophones at one time. Synthesis of the receiving array from a single hydrophone would eliminate the need for substantial redundant hardware.